JPH0381207B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking servo circuit for an optical disc player such as a digital audio disc player or an optical video disc player.

As this type of tracking servo,
There is a so-called push-pull method as shown in FIGS. In FIG. 1, a light beam generated from a laser diode 1 passes through a polarizing beam splitter 3, is converted into a parallel beam by a collimating lens 4, and reaches a quarter-wave plate 5. Here, the linearly polarized light is converted into circularly polarized light, which is focused into a spot by a condensing lens 6 and irradiated onto a reflective film surface 8 of an optical disk 7 so as to form a focal point 9. Since pits 10 are carved on the reflective film surface 8, when the pits are present, the laser beam is diffracted and scattered, and the amount of light focused on the condenser lens 6 changes.
Since these circularly polarized laser beams are reflected with the same rotation, the direction of rotation is reversed with respect to the direction of travel. This inverted laser beam passes through a quarter-wave plate 5, is converted into linearly polarized light, is focused by a collimating lens 4, is reflected by a polarizing beam splitter 3, and is then converted into linearly polarized light by a cylindrical lens 11. A pit image is formed on the split photodiode 12. This pit line is formed into a circle or an ellipse centered at the intersection with each division line X, Y of the four-division photodiode 12. Here, one dividing line X corresponds to a line along the moving direction of the pit 10, which moves in a direction parallel to the plane of the paper in FIG. When the pit 10 is shifted with respect to the laser beam focus 9, the center of the pit image is shifted with respect to one of the dividing lines X. Focusing on the deviation of the pit 10 with respect to the focal point 9, the amount of light received by each set of diodes a and b or the set of c and d of the four-part photodiode 12 with respect to the pit image obtained in this way is determined by the direct current component. It includes a relatively high frequency detection signal that is

Adders 13 and 13' add up the detected values of the light amounts of each set of diodes a and b or each set of diodes c and d for these sets. The subtracter 14 subtracts these added values from each other, and the subtracted results with positive and negative signs are sent to the phase correction circuit 15.
give to The phase correction circuit 15 corrects the phase relationship between the drive signal of the tracking coil 16 and the detection signal obtained from the condenser lens 6 based on the output of the subtracter 14. However, in the control circuit shown in FIG. 2, the output signal of the subtracter 14 includes the effects of surface runout and warping of the disk 7, so this becomes a tracking error signal and the tracking This was reducing control accuracy.

This invention is designed to perform highly accurate tracking control by minimizing the effects of surface wobbling or warping of the disk 7. The mutual square difference of the high frequency components of the amount of light detected from each photodiode set is determined and demodulated, this is low-passed, and the signal is output as a tracking error signal.

Embodiments of the present invention will be described below based on the drawings.

The control circuit of FIG. 3 is used in conjunction with the pickup unit of FIG. 1 in the same manner as in the control circuit of FIG. Quadrant photodiode 1
The sum a+b or c+d of each amount of light detected from each photodiode a, b or c, d forming one photodiode set divided by one dividing line Contains a relatively high-frequency detection signal superimposed on the DC component with respect to the progress, and the detection signal is divided by a dividing line ing. The first signal wave extractor 17 and the second signal wave extractor 17' calculate the sum a+b or c+d of the light amounts, respectively, and cut off the DC component to extract only the high frequency component. Here, if the high frequency components of the sums a+b and c+d of the respective amounts of light are respectively denoted as A and B, the adder 18 performs the calculation of A+B, and the subtractor 19 performs the calculation of AB. and multiplier 20
are the output A+B of the adder 18 and the output A of the subtracter 19
-B to calculate A ² -B ² and give this to the low-pass filter 21. The low-pass filter 21 extracts only the low frequency component and supplies it to the phase correction circuit 22 as a tracking error signal. The phase correction circuit 22 controls the current direction and current value of the tracking coil 16 based on the tracking error signal, thereby controlling the movement of the optical axis of the condenser lens 6 and the like.

The operation of the above configuration will be explained below. The output of the first and second signal wave extractors, that is, the sum a+b of the light amount of each diode a, b or c, d
Alternatively, the high frequency component A or B from which the DC component of c+d has been cut vibrates at a relatively high frequency while the center of vibration changes at a relatively low frequency to form a signal wave having positive and negative values. A ² or B ² calculated by the multiplier 20 is the magnitude of the amplitude of the high frequency components A and B that oscillate to positive and negative values, and A ² - B ² is the amplitude square difference. This amplitude 2
The multiplicative difference A ² −B ² similarly changes in low frequency while vibrating at high frequency, and only the low frequency change is extracted by the low-pass filter 21, which becomes a tracking error signal.

As described above, according to the present invention, calculations are performed using only high-frequency vibrations with the DC component cut out, so by cutting the DC component, the effects of surface runout and warping of the disk are eliminated, and thus the trouble is improved. Errors in the king error signal are reduced.

[Brief explanation of drawings]

FIG. 1 is an optical system layout diagram showing an example of a pickup unit of an optical disc player, FIG. 2 is a conventional tracking servo circuit diagram, and FIG. 3 is a tracking servo circuit diagram showing an embodiment of the present invention. 12... Quadrant photodiode, 20... Multiplier, 17, 17'... First and second signal wave extractor,
21...Low pass filter, 18...Adder, 19...
Subtractor.

Claims (1)

[Scope of Claims] 1. In a circuit that scans a row of pits on a disk using a light beam and performs tracking control by detecting the bias of the pits with respect to the light beam using a four-division photodiode, the dividing line of the four-division photodiode A first signal wave extractor that calculates the sum of the respective amounts of light detected from one set of photodiodes whose focal points are separated from each other by a dividing line along the moving direction of the pit, and extracts the high frequency component thereof. and a second signal wave extractor that calculates the sum of each light amount detected from the other photodiode set and extracts its high frequency component; the first signal wave extractor and the second signal wave extractor; an adder and a subtracter that calculate the sum and difference between the outputs of the adder and the subtracter, a multiplier that calculates the product of the outputs of the adder and the subtracter, and a low-pass output of the multiplier to track it. A tracking servo circuit for an optical disc player, which is provided with a low-pass filter that outputs an error signal.